Aims: Persistent halogenated organic pollutants (e.g., DDT, PCBs [polychlorinated biphenyls], dioxin) command special attention in public health because they are ubiquitous in the ecosystem and may be causing adverse human health effects at background levels of exposure, via diet. We are conducting several studies of the human health effects of background exposure to organochlorines. Accomplishments: We found that in utero DDE exposure was associated with a modest increase in cryptorchidism, hypospadias, and polythelia, though none of the results were statistically significant. We find no association of in utero PCB exposure with any of the neurodevelopmental outcomes that we have examined. The most notable finding so far has been that maternal pregnancy DDE levels were associated with increased risk of preterm birth and being born small-for-gestational-age. Compared with boys whose mother had a serum DDE level of < 15 mg/L (the lowest 20%), those whose mother had a serum level of 60 mg/L or more (the highest ~5%) had an adjusted odds ratio for preterm birth of 3.1, and an adjusted odds ratio for small-for-gestational-age of 2.6. Dose-response relations were present and trend tests were statistically significant. A report is in press. The relation between DDE and small size persisted at 7 years of age, even after adjustment for birth size. PCBs. We found essentially no relation between in utero PCB exposure and thyroid hormone levels in neonates. We found, however, an association of PCB levels with diabetes among pregnant women. TCDD. We found an association between TCDD level and prevalence of type 2 diabetes. In our analysis the 50% of the population with the highest TCDD levels had a risk of diabetes that was increased by about 80% compared to those with level in the bottom 25th percentile. Our findings were prominently featured in an Institute of Medicine report. Breast Cancer Study. The study is completed, and the data have been cleaned and edited. We will attempt to address why African-Americans, but not whites, would be at increased risk from PCBs . PCB Exposure Comparison Study. We found that the range of exposure was comparable in eight out of the ten studies. The median exposure level in the two remaining studies was about 3 times higher, and half as high, respectively, of the typical level. Variation in results on PCBs and neurodevelopment across studies appears to be due to factors other than the exposure levels.